We explore the world’s hidden and unknown artisan enclaves to find unique and affordable treasures that we are proud to share with you. That’s why we feel a special kinship with the authors of the book Atlas Obscura: An Explorer’s Guide to the World’s Hidden Wonders. These intrepid, curious Atlas Obscura explorers have unearthed 700 of the planet’s most haunting places: utterly unique destinations, true stories, unimaginable creations and thrilling natural occurrences.

But it’s not all baobab trees and baby jumping festivals. Sometimes Atlas Obscura uncovers true horrors and bizarre obsessions. In honor of Halloween, we’re treating you to the Atlas Obscura selection of the world’s most haunted and haunting places…

Read on, if you dare.

Cameroon, Lake Nyos, Menchum, Northwest Region

Lake Nyos killed over 1,700 people in a single night, but its victims did not drown. None were even in the lake. Many died in their beds, in homes up to 15 miles (24 km) from shore.

The bizarre disaster began with the buildup of carbon dioxide in the lake, which sits in the crater of a dormant volcano. Gas rose from an underground magma chamber and dissolved into Lake Nyos, slowly creating a highly pressurized bottom layer saturated with carbon dioxide.

On the evening of August 21, 1986, just after 9 p.m., the lake erupted. A huge cloud of carbon dioxide burst from the water, smothering local villages and asphyxiating the people and animals within them. Those who survived spent hours unconscious from oxygen deprivation. They awoke surrounded by bodies, with no indication of what had happened.

Since this catastrophic event, French scientists have implemented a degassing program at Lake Nyos. In 2001, they installed a pipe that runs to the bottom of the lake and allows the gas to escape at a regular, safe rate. Two more pipes were added in 2011. A solar-powered alarm system monitors carbon dioxide levels should the lake explode again, there will at least be some warning.

Park of the Monsters, Lazio, Italy

The stone sculptures in the Parco dei Mostri emerged from the tormented mind of 16th-century Italian prince Pier Francesco Orsini. Pier endured a brutal war, saw his friend killed, was held for ransom for years, and returned home only to have his beloved wife die. Seeking a way to express his grief, Orsini hired architect Pirro Ligorio to create a park that would shock and frighten its visitors.

The park exhibits the 16th-century Mannerist style an artistic approach that rejected the Renaissance’s elegance and harmony in favor of exaggerated, often tortured expressions and a mishmash of mythological, classical, and religious influences. Its wretched sculptures — including a war elephant attacking a Roman soldier, a monstrous fish head, a giant tearing another giant in half, and a house built on a tilt to disorient the viewer — caught the attention of Salvador Dalí, who visited in 1948 and found much to inspire his surrealist artwork.

A trip to the park is not complete without a walk up the stone stairs leading into the “Mouth of Hell” — the face of an ogre captured midscream. Walk into its gaping maw, inscribed with “all reason departs,” and you’ll find a picnic table with benches. Localita Giardino, Bomarzo. From Rome take a train to Orte Scalo, where you can switch to a bus to the gardens.

Skeleton Lake, Uttarakhand, India

When park ranger H. K. Madhwal discovered a lake ringed with thousands of human bones while walking in the Uttarakhand Himalayas in 1942, he raised a question that went unanswered for over 60 years: what killed the hundreds of people whose skeletons surrounded the lake? At first, the bones were thought to belong to Japanese soldiers who had stealthily crossed into India during World War II and perished in the high-altitude conditions. But carbon dating during the 1960s showed the estimated death date was wrong — very wrong. A broad range from the “12th to 15th century” was the best possible guess, but no cause of death could be established.

In 2004 the world got an answer to the mystery of Skeleton Lake. Radiocarbon testing at Oxford University narrowed the date of mass death to 850 BCE, give or take 30 years. Analysis of skulls showed that, no matter their stature or position, all of the people died in a similar way: from blows to the head. The bodies had wounds only on their heads and shoulders, indicating the blows came from directly above.

After dismissing earlier theories, which included ritual suicide and attacking hordes, the scientists reached an unexpected conclusion: The travelers died from a severe hailstorm.

Hail is rarely lethal. But trapped in a valley without shelter and given no warning of the storm’s severity, the 9th-century BCE travelers could not escape the sudden barrage of tennis-ball-size spheres of ice.

Twelve hundred years after the storm, the green-tinged bones of hail victims still ring the lake, preserved alongside skulls and tattered shoes at an altitude of 16,500 feet (5,029 m).